JPS6021404B2 - A device for generating a signal for intensity modulation of a light beam in an optical recording device - Google Patents

Description

[Detailed Description of the Invention] Research and development has been actively conducted on technology for recording various types of information at high density using disk-shaped information recording media (hereinafter sometimes referred to as disks) and reproducing the information. As a result, the applicant's company is also promoting research and development on high-density recording and reproducing methods using various types of disks, as well as research on their practical application.

When attempting to record information signals at high recording density on the source disc of a disc, a typical recording method that has been used from the beginning is to use a minute spot of a laser beam modulated by the information signal. Alternatively, a minute spot of an electron beam modulated by an information signal is irradiated onto the beam-sensitive material layer (for example, a photoresist layer) of the master disc. Since the recording means used requires the use of expensive equipment, an inexpensive optical recording means using a laser beam may be used unless the rotation speed of the disk is set low. many.

By the way, when an information signal is recorded on a recording medium by an arrangement of bits corresponding to the information signal, in order to prevent distortion in the reproduced signal from the recording medium, it is necessary to It is necessary that the shape of the bits and the manner in which the bits are arranged are set in a predetermined manner.

If the recording medium is a disc, the recording and reproducing method of information signals on the disc, the number of revolutions of the disc, the recording area of the disc, the frequency band of the information signal (recorded signal), etc. are determined in advance, and the short recording wavelength formed on the disc corresponding to the recording signal is determined by a signal indicating the highest frequency value of the recording signal at the recording trace position on the inner circumference of the recording area of the disc. arise.

Assume now that the disk is rotating at IQ rotation per second, and that the recording track position on the inner circumference of the recording area of the disk is a distance of 5 points from the center of the disk, and furthermore, the recording signal Considering the case where the highest frequency of is 1 Sengawa z, the shortest recording wavelength of the recording signal on the disk is about 0.5 Sengawa z.

On the other hand, when recording an information signal onto a recording medium optically, recording is performed by irradiating a photosensitive layer such as a photoresist layer with a focused spot of light whose intensity is modulated by the recording signal. However, as the photoresist that should constitute the photoresist layer, one having characteristics that can form a required recording pattern based on the recording signal is used. The light source for obtaining the light to be irradiated onto the photoresist layer is one that can easily and stably emit light of a wavelength that can satisfactorily sensitize the photoresist used in the composition of the photoresist layer. A light source with a wavelength of 4579 angstroms is required as a light source that can generate high output with a high S/N ratio. One example is that a laser light source that generates a beam of light is used.

By the way, the diameter of the condensed spot obtained when light is condensed is determined by the function number (NA) of the optical system for condensing the light and the wavelength of the condensed light. For example, if the wavelength of the light to be formed is 4579 angstroms and the closure number of the optical system for focusing the light is 0.9, the diameter of the focused spot is 0.6 in terms of the Airy disk diameter.
The width at half maximum is 0.27.

4. Now, if we consider the case where a recording signal with a short recording wavelength of 0.5 mm as described above is recorded on a recording medium by intermittent light by the recording signal, the highest frequency in the recording signal When recording a signal indicating , a movement locus of a focused spot over a skin length of approximately 0.25 mm is recorded on the recording medium, followed by a non-irradiated portion of light over a length of approximately 0.25 rw. They must be formed alternately on the medium, but as in the example above, the wavelength of the light used for recording is 4579 angstroms, and the function factor of the optical system for focusing the light is 0.9. In this case, the focused spot diameter is 0.6rm (Eary disk diameter) and the half width is 0.2.
Since there are 7 peaks, the shortest recording wavelength on the recording medium is 0.5 cm as in the above example using such a light spot.
It is difficult to properly record a recording signal with a wavelength of 500 nm on a recording medium, and in conventional disks, the recording wavelength is particularly high on the inner circumferential side of the disk where the recording wavelength on the disk is short. The problem was that the shape and arrangement pattern of the bits formed in correspondence with the recorded frequency signal were not correct, and distortion occurred in the reproduced signal. The applicant company has shortened the recording wavelength on the disk so that the recording pattern by bits shows a duty factor of 50%, and the depth of the bits is also a predetermined depth. The above problems could be solved by adopting a new optical recording method to prevent the above problems from occurring.

That is, in the applicant company, when a recording signal is optically recorded on a recording medium by irradiating the recording medium with a focused spot of light that is interrupted by the recording signal,
As the recording wavelength represented on the recording medium by a pair of light irradiation sections and light cutoff sections that are intermittent by the recording signal becomes shorter, the length of the light irradiation section becomes larger than the recording wavelength. The information signal is recorded on the recording medium in such a way that the ratio, and is gradually decreased, and the intensity of the light on the recording medium in the light irradiation section is approximately equal regardless of the recording wavelength. By doing this, the above-mentioned problem was solved. In implementing the new optical recording method proposed by the applicant company, the optical recording method is represented on the recording medium by a pair of light irradiation sections and light cutoff sections that are interrupted by a recording signal. As the recording wavelength becomes shorter, it is necessary to gradually reduce the ratio of the length of the light irradiation section to the recording wavelength. The purpose of this invention is to easily provide a method for generating a signal for modulating the intensity of a light beam in an optical recording device that is suitable for implementing a new optical recording method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific details of the method for generating a signal for intensity modulation of a light beam in an optical recording apparatus of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a schematic configuration of an optical recording device including the device of the present invention, and in FIG. 1, SG is a signal source of a signal to be recorded, In the following explanation, the signal source S of the horizontal whip signal to be recorded is
Although it is assumed that a video signal is sent from G,
Of course, the information signal to be recorded may be an information signal other than a video signal, such as a PCM signal or other signals. The video signal sent out from the signal source SG of the information signal to be recorded is fed to a frequency modulator FMOD';
The FM wave signal frequency-modulated by the video signal is applied to the non-inverting input terminal of the comparator COMP. Further, the video signal sent from the signal source SG of the information signal to be recorded is also given to a variable gain amplifier VCA (voltage control amplifier VCA), and this variable gain amplifier VC
For the video signal amplified by A, the potential at the tip of its horizontal synchronizing signal is set in advance in the clamp circuit CCT.
After being clamped at a predetermined fin position, it is applied to the inverting input terminal of the OMP to the above-mentioned comparator. The gain of the variable gain amplifier VCA described above is controlled by a control voltage generated by a control voltage generator CSG, and
The clamp voltage in the clamp circuit CCT is also generated by the control voltage generator CSG.

The control fin pressure generation circuit CSG is an optical system that is moved in the arrow x direction in the figure so that the condensed spot irradiated on the disc D is moved in the arrow x direction in the figure in the direction of the disc. It is configured so that a required control voltage can be generated in accordance with the movement of the system L. Now, the frequency modulator FMO
The instantaneous frequency value of the FM wave signal applied from D to the non-inverting input terminal of the comparator COMP, that is, the FM wave signal frequency-modulated by the video signal, is the same as the video signal applied as a modulated wave to the frequency modulator FMOD. It is well known that the video signal corresponds to the voltage value of the signal, but now the video signal is of positive polarity (the voltage value of the signal part corresponding to the black of the image is small, In the case of a video signal in which the voltage value is large in the video signal, and in the case of a signal in which the synchronization signal is projected in the black direction than the black in the video signal, the frequency is increased by the video signal. The low instantaneous frequency part of the modulated FM wave signal corresponds to the voltage value at the tip of the synchronization signal inserted into the video signal.
Furthermore, the high instantaneous frequency portion corresponds to the 100% white portion of the video signal.

Therefore, the FM wave signal frequency-modulated by the video signal having the above-mentioned signal form is transmitted to the optical modulator PM.
V is supplied to the OD as a modulation signal, the laser light beam entering the optical modulator PMOD from the laser light source is intensity-modulated by the optical modulator PMOD, and the transmitted light from the optical modulator PMOD is transmitted through the imaging lens. A light beam formed on the disc D by intermittent light beams is applied as a condensed spot onto the photoresist layer on the disc ○ through the optical system L that includes the optical system L. The recording wavelength of the signal to be recorded is the longest in the part corresponding to the leading edge of the synchronization signal in the video signal, and the recording wavelength in the video signal is the longest.
The part that corresponds to the 0% white part has a short technique.

Also, since the disk D is rotated by the motor M at a constant rotation speed, as the focused spot moves in the horizontal direction, the relative linear velocity between the focused spot on the disk ○ and the disk D is as follows. It changes in proportion to the distance between the center of disk D and the focused spot, so even if the light is interrupted at the same frequency value, it will not be recorded on disk D. The recording wavelength of the signal becomes gradually shorter from the outer circumferential side to the inner circumferential side of the disk D.

Therefore, when an information signal is optically recorded by irradiating the disk with a bright spot of light that is interrupted by an intensity modulating signal of a light beam in the form of an FM wave signal that is frequency-modulated by the information signal to be recorded. As the recording wavelength represented on the disk becomes shorter by the pair of light irradiation sections and light cutoff sections that are intermittent by the light beam intensity modulation signal, the light irradiation section becomes shorter with respect to the recording wavelength. In order to make the occupied length ratio as small as required, it is necessary to obtain information about the pressure value of the video signal used as the information signal to be recorded and the focused spot on the disk D. by both information regarding the location of
It is necessary to be able to vary the duty factor of the signal for intensity modulation of the light beam as required.

For this purpose, in the embodiment shown in the first figure, a control mechanism is based on information on the movement of the optical system including the imaging lens L, that is, information on the position of the condensed spot in the direction of the disc ○. The voltage is generated by the control voltage generator SG to control the amplification degree of the variable gain amplifier VCA and the clamp circuit CCT.

Figure 2a is a waveform diagram of the FM wave signal {Figure 2a} that is supplied to the non-inverting input terminal of the OMP to the comparator.
In addition, in Figures 2b to d, the signal levels of the signals supplied to the inverting input terminal of the same device COMP are respectively bb, c-c, and dd in Figure 2a. This is a waveform diagram of a rectangular wave output from OMP to a comparator when becomes the changed one.

As mentioned above, the recording wavelength is shortened on the disk ○,
Since it is the signal portion (white portion) with a large voltage value in the video signal that causes recording, the duty factor of the modulation signal that is to form the recording and the armor of the recording wavelength on the disk is small. To make the frequency modulator F
It is sufficient to set the amplitude of the video signal supplied to the MOD to an appropriate value and apply it to the comparator at the inverting input terminal of the OMP. is supplied to the inverting input terminal of the comparator COMP via the variable gain amplifier VCA (the clamp circuit CCT will be described later). The variable gain amplifier VCA is used to vary the amplitude of the video signal supplied to the inverting input terminal of the comparator COMP by the control voltage generated by the control voltage generator CSG. As the position of the focused spot moves from the outer circumferential side to the inner circumferential side of the disk D, even signals of the same frequency are recorded as having gradually shorter recording wavelengths. Relatedly, by changing the amplitude of the video signal to be supplied to the inverting input terminal of the OMP to the comparator, even when recording signals of the same frequency, the position of the light spot changes from the outer circumference of the disk to the inner circumference. This is so that the duty factor of light interruption can be gradually reduced as the light is moved to the side.

The video signal amplified by the variable gain amplifier VCA is clamped in the clamp circuit CCT so that the fin pressure value at the tip of the horizontal synchronization signal in the video signal is clamped to the crab pressure value set in the control voltage generator by SG, and then sent to the comparator. It is connected to the inverting input terminal of OMP.

As mentioned above, in the clamp circuit CCT, the voltage value for clamping the leading edge of the horizontal synchronization signal is generated in the control voltage generator SG by the synchronization signal which is recorded at a long recording wavelength on the disk D. In terms of parts, if the pupil of the light-building spot moves closer to the inner circumference of the disk D and the recording wavelength becomes shorter, it may be necessary to reduce the duty factor. It is from. The mode of generation of the control voltage to be generated by the control voltage generator CSG according to the position of the focused spot is as follows:
Even if the control voltage is generated in proportion to the moving distance of the condensed spot in the vertical direction, or
There are three cases in which the focal spot is in an area on the outer circumference side of the disk D, in an area between the outer circumference and the inner circumference of the disk D, and when it is in an area on the inner circumference side of the disk D. Thus, even if a different control voltage is generated for each recording area in a plurality of divided recording areas, any other generation mode may be adopted.

Now, for example, on the outermost side of the disk, the duty factor of the video signal and the corresponding signal remains unchanged at 50%, and on the middle part between the outer and inner circumference of the disk, The duty factor of the signal corresponding to the 100% white signal portion of the video signal is set to 40%, and the duty factor of the signal corresponding to the synchronization signal remains unchanged at 50%. Now, the duty factor of the signal corresponding to the 100% white signal part of the video signal is 30%, and the signal for intensity modulation of the light beam is set so that the duty factor of the signal part corresponding to the synchronization signal is 40%. When generating, first, if the light-forming spot is on the outer circumferential side of the disk, a control voltage is applied from the control voltage generator CSG to the variable gain amplifier VCA to set its gain to 0, and The clamp fly pressure is also 0 for the clamp circuit CCT.
volts is supplied, thereby providing an input of 0 volts to the inverting input terminal of the comparator COMP, causing the comparator to output OMP.
A square wave with a duty factor of 50% is output over the entire frequency range on the output side.

Next, when the focused spot is located at the outer periphery, inner periphery, and intermediate area of the disk, the clamp fin pressure applied from the control voltage generator CSG to the clamp circuit CCT is still 0 volts, but the control From the SG to the voltage generator to the variable gain amplifier VCA, the variable gain amplifier VCA
When the voltage value of the 100% white signal portion of the video signal output from the OMP is applied to the comparator at the inverting input terminal of the OMP, the duty factor of the square wave appearing at the output side of the OMP is set to 40% by the comparator. A control fin pressure is provided such that the gain of the variable gain amplifier is set such that an output video signal is output from the variable gain amplifier VCA such that the output video signal can be controlled.

As a result, when the focused spot is repositioned to the intermediate area between the outer and inner peripheries of the disc, the signal corresponding to the 100% white signal portion in the video signal has a duty factor of 40%, and the synchronization signal The signal corresponding to the part is made with a duty factor of 50% and the light modulator PMOD
is supplied to Furthermore, when the focused spot is located in the inner circumference area of the disk, the clamp voltage at the tip of the horizontal synchronization signal causes the comparator to generate a rectangular wave with a period corresponding to the horizontal synchronization signal period appearing on the output side of the OMP with a duty shift. The duty factor is 40%, and the rectangular wave appearing at the output side of the comparator COMP corresponds to the voltage of the 100% white signal portion in the output video signal of the variable gain amplifier VCA, and the duty factor is 30%. A control voltage for causing this is supplied from the control fin pressure generator CSG to the clamp circuit CCT and the variable gain amplifier VCA, respectively.

A bias voltage is applied to terminal B of the optical modulator PMOD to bring the optical modulator PMOD into a proper operating state, and a signal for modulating the intensity of the optical beam from the OMP is sent to the optical modulator PMOD by the above-mentioned comparator. When installed, the optical modulator PM
The OD intermittents the laser light according to the modulation signal, and
On the top, recording is performed using a condensed spot condensed by an imaging lens.

In this way, the above-mentioned new optical recording method can be achieved by applying the modulation signal obtained by generating the signal for intensity modulation of the light beam of the present invention to the optical modulator to modulate the intensity of the laser light beam. This can be carried out well, and the information signal recorded by the bit arrangement can easily have a duty factor of 50% regardless of the length of the recording wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an optical recording device equipped with a signal generator for intensity modulating a light beam according to the present invention, and FIGS. 2A to 2D are explanatory waveform diagrams.

SG... Signal source of information signal to be recorded, FMOD...
...Frequency modulator, COMP...Comparator, C
CT...clamp circuit, VCA...variable gain amplifier, CSG...control voltage generator, LS...
...Laser light source, PMOD...Light modulator, L
......Imaging lens, D...Disc, T...
Turntable, M...Motor.

Strategy 1 diagram Figure 2

Claims (1)

[Claims] 1 FM frequency modulated by the information signal to be recorded
When an information signal is optically recorded on a disc-shaped recording medium, the light beam is As the recording wavelength represented on the recording medium becomes shorter by a pair of light irradiation sections and light cutoff sections that are intermittent by the intensity modulation signal, the light irradiation section becomes shorter with respect to the recording wavelength. A device for generating a signal for intensity modulation of a light beam in an optical recording device in which the proportion of the length occupied by the light beam is small, and means for obtaining an FM wave signal frequency-modulated by an information signal to be recorded. a means for amplifying an information signal to be recorded by a variable gain amplifier whose gain is variably controlled by a control signal generated in accordance with a recording position on the disc-shaped recording medium; and a recording position on the disc-shaped recording medium; means for clamping a particular signal level portion of the output signal from the variable gain amplifier with a correspondingly generated predetermined clamp voltage;
means for adding the output signal from the variable gain amplifier in which a portion of a specific signal level is clamped to a predetermined potential by the aforementioned clamping means and the aforementioned FM wave signal, and for waveform shaping; A device for generating a signal for intensity modulation of a light beam in an optical recording device.